The invention relates to a device for cooling an electrical machine, in particular an electric motor, wherein the electrical machine has a stator with a stator core as well as a rotor with a rotor core which is seated on a rotor shaft. Coil windings with axially projecting end windings are incorporated in the stator core.
The invention also relates to an electrical machine, in particular to an electric motor with a cooling device such as this, in particular for cooling at least one end winding and/or the rotor shaft in the axial area of the at least one end winding.
Electrical machines, in particular electric motors such as asynchronous motors or synchronous motors, are required for a wide range of drive tasks, for example for driving machine tools. Electrical machines produce heat losses during operation, as a result of electrical losses such as eddy current or copper losses. Increased cooling of the electrical machine may be necessary if the heat losses that occur cannot simply be dissipated to the surrounding area via the outer surface of the electrical machine.
Electrical machines may be cooled by a gaseous or liquid medium. Air is preferably used as a gaseous medium, and water as a liquid medium. Electrical machines may be self-cooled or externally cooled.
In the case of self-ventilated machines, the electrical machine is typically cooled by an impeller wheel seated on a shaft end of the electrical machine. In the case of externally ventilated electrical machines, the cooling is provided by means of a separate fan, which produces a cooling air flow independently of the rotation speed of the electrical machine. In order to cool the electrical machine, the air can flow through the air gap between the stator and the rotor, through cooling air channels which run axially in the stator and/or rotor, or by means of a cooling jacket on the radial outer face of the electrical machine.
In the case of liquid cooling, the electrical machine is preferably cooled by means of a cooling jacket. This is necessary in particular for built-in motors or motor spindles with a relatively high power density. In the case of motors such as these, cooling via the outer surface in the installed state is possible only to a restricted extent.
Components or parts of the electrical machine which become particularly hot during operation, for example the end winding of a coil winding which is laid in the stator core, are coupled to the liquid-cooled cooling jacket with as low a thermal transfer resistance as possible. In the case of the end winding, this is done via a thermally conductive encapsulation compound. The end winding is embedded or encapsulated in the encapsulation compound. The thermally conductive encapsulation compound therefore rests over an area, and in particular flush, on the cooling jacket.
Nevertheless, even when using this cooling method, the hot spots in the motor interior, for example in the end winding and in the rotor shaft, are cooled only inadequately. This has the disadvantageous consequence that the electrical machine must be derated for relatively long-term operation, in order to avoid overheating.